Fiber-optic sensors and sensing systems are frequently used to detect the presence and monitor the concentration of various analytes, including oxygen, carbon dioxide, and hydrogen ions (i.e., pH), in both liquid and in gas environments. Such sensors are based on the recognized phenomenon that the absorbence and, in some cases, the luminescence, phosphorescence, or fluorescence of certain indicator molecules are perturbed by the presence of specific analyte molecules in the environment. The perturbation of the light emission properties and/or absorbence profile of an indicator molecule can be detected by monitoring radiation that is absorbed, reflected, or emitted by it when illuminated in the presence of a specific analyte.
Fiber-optic sensors that position an analyte sensitive indicator molecule in a light path optically monitor the effect of the analyte on the indicator molecule. Typically, for monitoring carbon dioxide, pH level, or some other parameter in a particular environment, an optical fiber transmits electromagnetic radiation from a light source to the indicator molecule, and the level of absorbence as measured by the light reflected from the vicinity of the indicator molecule gives an indication of the gaseous or ionic concentration of the analyte. These indicator molecules are typically disposed in a sealed chamber at the distal end of the optical fiber, and the chamber walls are permeable to the analyte of interest.
Fiber-optic sensors are commonly used to monitor the blood gas parameter of a patient where the sensor is located at the end of a catheter that is inserted into the patient. One problem with such sensors is that the optical fibers attached to the end of the sensor are prone to kinking. The optical fibers are delicate because they are situated as an external appendage located at the end of the catheter used to invasively insert the sensor and extend distally beyond it. Any mishandling of the catheter or movement of the patient can easily result in kinking of the optical fibers.
In view of the importance of accurately measuring parameters such as carbon dioxide, oxygen, and pH, there is an existing need to provide a method and apparatus that provides accurate and timely measurements of the parameters being monitored regardless of a kink in the optical fibers. At the very least, the method and apparatus should notify the operator when a kink occurs. The present invention provides a simple and elegant method for detecting and compensating for a kink in an optical fiber that provides accurate and timely measurements, and in the alternative, issues a warning when a kink occurs.